In association with miniaturization and development of high integration of various semiconductor devices, the influence of various contaminants such as a particle, an organic matter, acid and basic substances, and the like, due to manufacturing environmental factors in a clean room, on the silicon wafer which is carried in a device process, is becoming more problematic.
With regard to this situation, in the semiconductor process, with the wafer diameter having become 300 mm in particular, a system called local-environment (mini-environment) which houses the silicon wafer in a closed container, and carries between manufacturing apparatuses and stores have come to be employed. A substrate storage container made of a plastic mainly is used widely as the transport and storage container.
Specifically, the substrate storage container is formed using of a synthetic resin such as a polypropylene, a polycarbonate, a cyclic olefin polymer, or the like. In particular, as a storage container for housing the 300 mm wafer (substrate), the storage container made of a polycarbonate resin is used mainly, because it has a high rigidity and the inside is visible.
Further, when using the substrate storage container, in order to prevent oxidation of the substrate surface to be housed therein and promotion of excess reaction during processing, and to prevent contamination due to adhesion of organic substances through water, it is proposed to replace the gas inside the substrate storage container with an inert gas such as nitrogen gas or dry air.
By using such a substrate storage container, the influence of various contaminants such as a particle, an organic matter, acid and basic substances, and the like, due to manufacturing environmental factors in a clean room can be reduced, as disclosed in Japanese Laid-open Patent Application Publication No. 2009-246154, for example.
However, on the other hand, in recent years, with increasing miniaturization of circuit patterns, in a metal process among device processes for example, it is becoming apparent that a relative humidity, that is, water content in the surrounding environment of the wafer, has great influence on the yield. It is necessary to reduce the relative humidity by substituting (purging) the air in the internal closed space of the substrate storage container with dry nitrogen or the like, and then to make it possible to keep low the relative humidity in the internal closed space of the substrate storage container as it is for a long period of time. In this respect, because the water absorption of the polycarbonate which has been mainly used as a material of the conventional substrate storage container is high, it is difficult to keep low the relative humidity in the internal closed space of the substrate storage container as it is for a long period of time after reducing the relative humidity by substituting (purging) the air in the internal closed space of the substrate storage container with dry nitrogen or the like.